hey, congrats on the new purchase of a lexus! that is such an awesome car. from what i gather, you want to lower the car with this new shock/spring setup. i wouldn't limit my choices to those of trd and bilstein. TEIN Coil-Over Suspension, Intrax Coil-Over Suspension, Eibach Springs, Intrax Springs, all make good springs for the lexus. and KYB makes a good shock for you car also. these parts can be picked up from Rod Millen Motorsports (www.rodmillen.com)
my experience with tuning cars is pretty great. i own a 96 gs300 with a twin turbo setup, HKS turbos, front mount intercooler, and Blitz blow off valves and exhaust. the handling side of the car is taken of by a tein coil over setup. coilovers will cost a signifigant amount more than the typical set of springs, but its adjustability for street, track (quarter mile or road course), and ability to be rebuilt best suits my needs. before that, i had eibach springs with the KYB shocks. those are adjustable units, and they maintain the lexus's supple ride, while still keeping the car firm, and reducing body roll. most all shocks come with a lifetime warranty.
good luck hunting...email me when you get hooked up with your setup! ([email protected]